Narrative:

Minimum rest overnight. I had to wait and get breakfast for 117 rest; so the captain did the entire preflight. I showed up at the time designated by scheduling. It was the first flight with this captain. He had completed the walk around and was finishing up the preflight when I showed up. He tested the fire system and the number 2 fire handle and overheat wasn't lighting. We isolated the problem to the a loop and he called up dispatch/mx control to defer it. We deferred it and put the selector switch in B per the MEL and everything tested normally; nothing to note for the rest of the time on the ground. Everything else went normal and was what would be expected from a new crew.fast forward to departure: we took off normal and were climbing out of about 18;000 ft. We started seeing a caution light flickering off and on. We went on the light hunt and saw the fault light and the number 2 engine overheat light flickering off and on. We sat on our hands and watched it for a couple of seconds both trying to figure out individually how we wanted to proceed. The lights kept coming off and then we started getting quick hits of the fire bell. We canceled the bell while we started talking about what to do. Do we do the memory item for the fire bell that's not even lighting because it's going out so fast? Do we do the overheat that's on for about 1/2 a second; or do we do the fault light that's alternating with the overheat? We figured that since we had just done the deferral on the one loop; it had an overwhelming chance of being just a fault so we started there. We asked ATC if we could level at FL300 due to a mx checklist. Fault light checklist didn't take us anywhere. There's a fault in the system; great. Lights were still flickering off and on with an occasional fire bell. We discussed continuing on for about 10 seconds and decided there was no way we were going to fly the flight holding down the fire bell cancel. Ok now what? We know the fire checklist but are sure it's a false indication so let's see where overheat goes before we go shut this down. Overheat checklist has the throttle come back and if the light goes out you're done. We try that and we need to go almost all the way to idle but the lights all stop. Push the power up and the lights start flickering off and on again. Problem solved. The captain said ok; let's divert to ZZZ. I briefly brought up ZZZ1 which we just left as clear and ZZZ and reduced visibility just to get ideas out. We looked at the weather from ZZZ and it was only 6 and HZ with few clouds; and it appeared to be closer. We elected to go there. I asked him if he wanted to make the radio call so that he could say what he wanted rather than doing the cockpit relay. He agreed. He [advised ATC]; stated something about the engine; and that we would need to divert to ZZZ but that no other assistance at this time was required. I messaged dispatch something to the effect that we were having an issue with an intermittent overheat on number 2 and were operating at reduced thrust and were diverting to ZZZ. ATC gave us vectors for the arrival; and we both tried to divide our attention between monitoring the aircraft and trying to get the box set up. ATC kept us on vectors until we had things programmed and figured out where we were on the arrival. About this point I noticed that we were getting slower than bugged and the power on the left side was at max. I suggested lower and we got it which helped a lot with speed and the asymmetrical control. Somewhere around here; the captain briefed the flight attendants on what was going on and also said something to the people. I was monitoring the aircraft and setting up both sides for the ILS into ZZZ and programming the performance computer. Dispatch messaged us back and said that we should be able to continue with a reduced thrust. I replied that we were at idle. Dispatch replied ok diverting to ZZZ and that they would let the station know. The captain called for thesingle engine approach checklist. We did that. The fas called up just to offer their perspective. They were noticing the yaw and said it was uncomfortable. They also said that the aircraft seemed to rattle a lot more than usual on takeoff. I told them the reason for the yaw and that was normal for the situation and passed the info on about the takeoff to the captain. The approach into ZZZ was normal other than it was flaps 15. We taxied into the gate and shut down the engine at the normal time. I kind of got a weird smell when we parked that lasted for about 10 seconds; but didn't think much of it. Mx took over the aircraft and we swapped to another with our people and continued onto [our destination]. Fast forward two legs and the captain got a call from the chief pilot. The overheat apparently was real.

Related reports:

Google
 

Original NASA ASRS Text

Title: B737 First Officer reported an overheat on the number two engine. Indications to the crew were ambiguous making it difficult to choose required action. The crew elected to divert and landed normally with the number two engine at idle.

Narrative: Minimum rest overnight. I had to wait and get breakfast for 117 rest; so the Captain did the entire preflight. I showed up at the time designated by scheduling. It was the first flight with this Captain. He had completed the walk around and was finishing up the preflight when I showed up. He tested the fire system and the number 2 fire handle and overheat wasn't lighting. We isolated the problem to the A loop and he called up Dispatch/MX Control to defer it. We deferred it and put the selector switch in B per the MEL and everything tested normally; nothing to note for the rest of the time on the ground. Everything else went normal and was what would be expected from a new crew.Fast forward to departure: We took off normal and were climbing out of about 18;000 FT. We started seeing a caution light flickering off and on. We went on the light hunt and saw the Fault light and the number 2 Engine Overheat light flickering off and on. We sat on our hands and watched it for a couple of seconds both trying to figure out individually how we wanted to proceed. The lights kept coming off and then we started getting quick hits of the fire bell. We canceled the bell while we started talking about what to do. Do we do the memory item for the fire bell that's not even lighting because it's going out so fast? Do we do the overheat that's on for about 1/2 a second; or do we do the fault light that's alternating with the overheat? We figured that since we had just done the deferral on the one loop; it had an overwhelming chance of being just a fault so we started there. We asked ATC if we could level at FL300 due to a MX Checklist. Fault Light Checklist didn't take us anywhere. There's a fault in the system; great. Lights were still flickering off and on with an occasional fire bell. We discussed continuing on for about 10 seconds and decided there was no way we were going to fly the flight holding down the fire bell cancel. Ok now what? We know the Fire Checklist but are sure it's a false indication so let's see where overheat goes before we go shut this down. Overheat Checklist has the throttle come back and if the light goes out you're done. We try that and we need to go almost all the way to idle but the lights all stop. Push the power up and the lights start flickering off and on again. Problem solved. The Captain said ok; let's divert to ZZZ. I briefly brought up ZZZ1 which we just left as clear and ZZZ and reduced visibility just to get ideas out. We looked at the weather from ZZZ and it was only 6 and HZ with few clouds; and it appeared to be closer. We elected to go there. I asked him if he wanted to make the radio call so that he could say what he wanted rather than doing the cockpit relay. He agreed. He [advised ATC]; stated something about the engine; and that we would need to divert to ZZZ but that no other assistance at this time was required. I messaged Dispatch something to the effect that we were having an issue with an intermittent overheat on number 2 and were operating at reduced thrust and were diverting to ZZZ. ATC gave us vectors for the arrival; and we both tried to divide our attention between monitoring the aircraft and trying to get the box set up. ATC kept us on vectors until we had things programmed and figured out where we were on the arrival. About this point I noticed that we were getting slower than bugged and the power on the left side was at max. I suggested lower and we got it which helped a lot with speed and the asymmetrical control. Somewhere around here; the Captain briefed the Flight Attendants on what was going on and also said something to the people. I was monitoring the aircraft and setting up both sides for the ILS into ZZZ and programming the performance computer. Dispatch messaged us back and said that we should be able to continue with a reduced thrust. I replied that we were at idle. Dispatch replied ok diverting to ZZZ and that they would let the station know. The Captain called for theSingle Engine Approach Checklist. We did that. The FAs called up just to offer their perspective. They were noticing the yaw and said it was uncomfortable. They also said that the aircraft seemed to rattle a lot more than usual on takeoff. I told them the reason for the yaw and that was normal for the situation and passed the info on about the takeoff to the Captain. The approach into ZZZ was normal other than it was flaps 15. We taxied into the gate and shut down the engine at the normal time. I kind of got a weird smell when we parked that lasted for about 10 seconds; but didn't think much of it. MX took over the aircraft and we swapped to another with our people and continued onto [our destination]. Fast forward two legs and the Captain got a call from the Chief Pilot. The overheat apparently was real.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.